1. Field of the Invention
The present invention relates to a space light modulating apparatus for modulating a space light by changing a phase, an amplitude, or the like of the light which passes and, more particularly, to a space light modulating apparatus in which a display screen is divided into stripe-like regions and a phase distribution of a hologram is electronically formed by a change in phase or amplitude of the transmitted light due to the control of microsegments arranged one-dimensionally every region, thereby displaying a solid image.
2. Description of the Related Art
A stereoscopic display using a hologram enables a structure of a depth, a thickness, and the like of a 3-dimensional object to be easily visually understood. Such a stereoscopic display is largely demanded in the display of a designed structural object, the display of a medical image, and the like. A solid image is impressive as compared with a 2-dimensional display and is also used in the display for an amusement in an amusement park, a movie, or the like.
Hitherto, a hologram to stereoscopically display an imaginary object cannot be formed by an ordinary hologram forming method whereby an object wave is interfered with a reference wave. Therefore, there is known a holographic stereogram method whereby 2-dimensional images when a 3-dimensional object is seen from various different directions are calculated from 3-dimensional shape data and a hologram interference fringe is sequentially recorded by a hologram interference exposure into stripe-like regions each having a microwidth in the horizontal direction and a width of screen in the vertical direction. According to the holographic stereogram method, however, a 2-dimensional image is fundamentally seen and the plane on which focal points of the eyes are located doesn't coincide with the position of an image that is observed due to a parallax of both eyes. Consequently, it is hard to see such an image, resulting in a cause of a fatigue. Particularly, in case of displaying an image at a position on this side than the screen, a burden on the eyes increases and a preferable stereoscopic display cannot be obtained.
To form a natural solid image (hologram) of an imaginary object, there is a method whereby a phase distribution (interference fringe) of the hologram is calculated from the 3-dimensional shape data and the calculated phase distribution and is recorded using a laser drawing apparatus or the like while spatially changing an exposure amount. Benton et al. who are professors at the Massachusetts Institute of Technology (MIT) have proposed a method of recording a hologram which is divided into stripe-like regions each having a width of screen in the horizontal direction and a microwidth in the vertical direction and in which only the parallax in the horizontal direction has been preserved in each region. A very large amount of calculations of the phase distribution of the hologram can be remarkably reduced by eliminating the parallax the vertical direction. As a hologram recording or reproducing apparatus, there is known a method whereby a modulated surface acoustic wave, namely, a moving interference fringe is generated by an acoustic optical element and the image of the interference fringes is set into a stationary state by the tracing operation of a scanning mirror. According to the hologram forming method by Prof. Benton et al., only the parallax in the horizontal direction is recorded into the divided stripe-like regions, so that it is advantageous when the interference fringes are calculated. However, such a method is a method of directly observing the hologram reconstruction image, so that there are problems such that the hologram interference fringes cannot be recorded as a hard copy onto a medium and a hologram cannot be reconstructed and displayed from the interference fringes recorded on the medium.
On the other hand, for example, as shown in FIG. 1, a method using a liquid crystal display in a display apparatus of a phase distribution of a hologram has been proposed as a trial to electronically reconstruct a hologram (JP-A-64-84993). FIG. 1 shows a liquid crystal display 100 having 36 (6 (vertical direction).times.6 (horizontal direction)) liquid crystal cells 102 for simplicity of explanation. A thin film field effect transistor (TFT) 104 is arranged in a non-transmitting region, shown by a hatched portion as a driving element in each liquid crystal cell 102. As shown in FIG. 2, the TFT 104 is constructed in a manner such that a voltage control line 106 in the horizontal direction arranged in a matrix form is connected to a source, a scan line 108 in the vertical direction is connected to a gate, and a drain is pulled up to a power source voltage V.sub.cc through the liquid crystal cell 102. When a control voltage is applied to the scan line 108 at a predetermined timing, the transistor 104 is turned on. Now, assuming that a control voltage of the control line 106 at this time is equal to V.sub.0, a voltage of (V.sub.cc -V.sub.0) is applied to the liquid crystal cell 102. Since a refractive index of the liquid crystal cell 102 changes in accordance with the applied voltage, an optical propagation distance changes, so that a phase or amplitude of the light which passes can be controlled.
However, in the case where a 1-dimensional hologram, which has been proposed by Prof. Benton et al., for instance, is electronically formed and displayed by such a conventional liquid crystal display, in order to reconstruct a perfect 1-dimensional hologram, a very large amount of information in the horizontal direction must be handled, so that an ultrahigh fine construction of the liquid crystal cell is needed. On the other hand, it is impossible to avoid an increase in number of driving elements to drive an extremely large number of liquid crystal cells in the display screen and various difficulties occur. Namely, as shown in FIG. 2, in the case where the TFT 104 is provided for each of the liquid crystal cells 102, when the liquid crystal cells are ultrahigh finely formed, it is difficult to form the TFT 104 to each region of the display screen as shown in FIG. 1. When a non-display region due to the formation of the driving element exists in the liquid crystal cell 102, a problem of the interference occurs between the liquid crystal cells 102 when the light passes.